Yoshida Riichiro, Umezawa Taishi, Mizoguchi Tsuyoshi, Takahashi Seiji, Takahashi Fuminori, Shinozaki Kazuo
Laboratory of Plant Molecular Biology, RIKEN Tsukuba Institute, 3-1-1, Koyadai, Tsukuba, Ibaraki 305-0074, Japan.
J Biol Chem. 2006 Feb 24;281(8):5310-8. doi: 10.1074/jbc.M509820200. Epub 2005 Dec 19.
ABI1 and ABI2 encode PP2C-type protein phosphatases and are thought to negatively regulate many aspects of abscisic acid (ABA) signaling, including stomatal closure in Arabidopsis. In contrast, SRK2E/OST1/SnRK2.6 encodes an Arabidopsis SnRK2 protein kinase and acts as a positive regulator in the ABA-induced stomatal closure. SRK2E/OST1 is activated by osmotic stress as well as by ABA, but the independence of the two activation processes has not yet been determined. Additionally, interaction between SRK2E/OST1 and PP2C-type phosphatases (ABI1 and ABI2) is not understood. In the present study, we demonstrated that the abi1-1 mutation, but not the abi2-1 mutation, strongly inhibited ABA-dependent SRK2E/OST1 activation. In contrast, osmotic stress activated SRK2E/OST1 even in abi1-1 and aba2-1 plants. The C-terminal regulatory domain of SRK2E/OST1 was required for its activation by both ABA and osmotic stress in Arabidopsis. The C-terminal domain was functionally divided into Domains I and II. Domain II was required only for the ABA-dependent activation of SRK2E/OST1, whereas Domain I was responsible for the ABA-independent activation. Full-length SRK2E/OST1 completely complemented the wilty phenotype of the srk2e mutant, but SRK2E/OST1 lacking Domain II did not. Domain II interacted with the ABI1 protein in a yeast two-hybrid assay. Our results suggested that the direct interaction between SRK2E/OST1 and ABI1 through Domain II plays a critical role in the control of stomatal closure.
ABI1和ABI2编码PP2C型蛋白磷酸酶,被认为对脱落酸(ABA)信号传导的多个方面起负调控作用,包括拟南芥中的气孔关闭。相反,SRK2E/OST1/SnRK2.6编码一种拟南芥SnRK2蛋白激酶,在ABA诱导的气孔关闭中起正调控作用。SRK2E/OST1可被渗透胁迫以及ABA激活,但这两个激活过程的独立性尚未确定。此外,SRK2E/OST1与PP2C型磷酸酶(ABI1和ABI2)之间的相互作用也不清楚。在本研究中,我们证明abi1 - 1突变而非abi2 - 1突变强烈抑制ABA依赖的SRK2E/OST1激活。相反,即使在abi1 - 1和aba2 - 1植物中,渗透胁迫也能激活SRK2E/OST1。在拟南芥中,SRK2E/OST1的C末端调节结构域是其被ABA和渗透胁迫激活所必需的。C末端结构域在功能上分为结构域I和结构域II。结构域II仅对SRK2E/OST1的ABA依赖激活是必需的,而结构域I负责ABA非依赖激活。全长SRK2E/OST1完全互补了srk2e突变体的萎蔫表型,但缺少结构域II的SRK2E/OST1则不能。在酵母双杂交试验中,结构域II与ABI1蛋白相互作用。我们的结果表明,SRK2E/OST1与ABI1通过结构域II的直接相互作用在气孔关闭的控制中起关键作用。